Studies will be continued on the regulation of T4 to T3 conversion in man and rat. In view of the demonstrated role of carbodhydrate on enhancing T4 to T3 conversion in rat liver homogenate, further studies on the role of lipid, protein, and branch chain amino acids on T3 and rT3 generation will be carried out. New studies on the effect of acute, large doses of dilantin administered to the hypothyroid rat on serum TSH and the TSH response to dilantin will be studied. Finally, studies on the hepatic generation of T3 in the dw/dw mouse and the effect of thyroid hormones on this generation will be studied.